The present invention relates to rotary fluid pressure devices such as low-speed, high-torque gerotor motors, and more particularly, to an improved lubrication flow circuit therefor.
A typical motor of the type to which the present invention relates includes a housing defining inlet and outlet ports and some type of fluid energy-translating displacement mechanism, such as a gerotor gear set. The typical motor further includes valve means to provide fluid communication between the ports and the volume chambers of the displacement mechanism. The invention is especially advantageous when used in a device wherein the displacement mechanism is a gerotor gear set including an orbiting and rotating gerotor star, and will be described in connection therewith.
In gerotor motors, an externally-splined main drive shaft (dogbone) is typically used to transmit torque from the orbiting and rotating gerotor star to the rotating output shaft. In order for the motor to have adequate operating life, it is important that these torque-transmitting spline connections be lubricated by a flow of lubricating fluid. It is also important that certain other elements of the motor be lubricated, such as any bearings which may be used to rotatably support the output shaft relative to the motor housing.
In certain prior art motors of the type described above, it has been known to provide a controlled amount of lubrication flow, in parallel with the main system flow path, by means of one or more metering notches defined by the rotary valve member, or by means of an extra amount of side clearance between the gerotor star and the adjacent housing surface. See for example, U.S. Pat. Nos. 3,572,983 and 3,862,814, both assigned to the assignee of the present invention. The lubrication flow is communicated from the main system flow path, at a location upstream of the gerotor gear set, thereby detracting from the volumetric efficiency of the motor. The resulting lubricant flow is "forward", i.e., toward the output shaft end of the motor, through the dogbone spline connections, and then through the bearings, and eventually to the outlet port.
In a recent improvement of the above-described lubrication arrangement, lubricant recesses have been provided in the end surface of the housing adjacent the internal teeth of a roller gerotor. These lubricant recesses cooperate with the clearance spaces at the ends of the gerotor rollers to generate a flow of lubricant which is then communicated to the lubrication flow path through the splines and bearings. See U.S. Pat. No. 4,533,302, also assigned to the assignee of the present invention.
Although the methods for providing lubricant flow described in the preceding two paragraphs have been in widespread commercial use and have been generally satisfactory, both methods have the disadvantage that the volume of lubricant flow is generally proportional to the load imposed on the motor, as represented by the pressure differential across the gerotor, or between the inlet and outlet ports. When a low-speed, high-torque gerotor motor is being operated at a pressure differential of 2,000 or 3,000 psi, and an output speed in the range of about 50 to 300 rpm, there typically is sufficient lubricant flow generated. However, during times when the motor is being operated at relatively high speed (e.g., 500 rpm), and at relatively low load (e.g., a pressure differential of about 500 psi), substantially less lubricant flow is generated. Unfortunately, it is during periods of such relative high-speed, low-load operation that greater lubricant flow is required because of the greater amount of rubbing action on elements such as the splines, caused by the higher speeds, and resulting in greater heat generation and an increase in contamination particles.
A solution to the above-described problem of insufficient lubrication during relatively high-speed, low-load operation is set forth in co-pending application U.S. Ser. No. 795,590, filed Nov. 6, 1985, in the name of Roland A. Dahlquist for a "gerotor motor and improved lubrication circuit therefor", now U.S. Pat. No. 4,645,438. The lubrication arrangement illustrated and described in the co-pending application provides a relatively constant flow of lubrication fluid, in parallel with the main flow path, and taken from the main flow path at a location downstream of the valving, such that the volumetric efficiency of the motor is not diminished.
The improved lubrication arrangement illustrated and described in the co-pending application does, however, have the disadvantage of requiring a separate case drain port. The lubrication fluid flows through the entire lubrication flow path, then to the case drain port and from there returns to the system reservoir. In many applications for motors of this type, the presence of a third port (i.e., the case drain port) and the associated hose and fittings, is considered undesirable by the vehicle manufacturer. This is especially true in situations where the motor is located somewhat remotely from the pump and reservoir, such that the length and cost of the hose from the case drain port back to the system reservoir becomes excessive. Also, because the case drain line is frequently a smaller and thinner hose, it is more susceptible to damage and leakage than the two main system lines.